Journal of food engineering vol:79 issue:2 pages:553-560
Visual colour degradation of tomato puree and strawberry juice at three different pH values (2.5, 3.7 and 5) during thermal (100140 degrees C, 0-120 min) and high pressure thermal (300-700 MPa, 60 min, 65 degrees C) treatments were studied. Hunter colour scale values L*, a* and b* of each treated sample were measured. Results indicated that the thermal degradation of tomato and strawberry colour followed first order kinetics (fractional conversion model). The L*a*/b* parameter combination described best the colour change of all samples. The activation energies for the different material were 129.12, 181.40, 162.60, 85.77 kJ/mol x 10(-2) for tomato puree, strawberry at pH 2.5, strawberry at pH 3.7, and strawberry at pH 5, respectively. Colour of strawberry at pH 5 was less heat stable but the degradation constants were less sensitive to temperature changes.